Here's why:
* Irreplaceable means something is so unique or valuable that it cannot be replaced if lost or damaged.
* Negative adjective refers to a word that describes a negative quality or characteristic.
Other possible words:
* Invaluable - This describes something that is extremely valuable and cannot be given a monetary worth.
* Priceless - Similar to invaluable, this emphasizes the impossibility of assigning a price to something due to its high value.
* Unique - This implies that something is one of a kind and therefore cannot be replaced.
These words all convey the idea of something being essential and impossible to substitute.